A simulation study on the effect of thoracic conductivity inhomogeneities on sensitivity distributions.

A high-resolution 3D finite difference model of the electrical conductivity distribution in a human thorax based on a 43-slice MRI data set along with lead field theory was used to examine the effect of thoracic conductivity inhomogeneities on sensitivity distributions. The electrode configurations used in the present study were based on an eight-electrode array positioned evenly around the thoracic model at a level close the nipple line. Sensitivity distributions of each possible adjacent pair current excitation pattern for both the homogeneous thoracic model and the heterogeneous thoracic model were evaluated. The results show that thoracic inhomogeneities significantly perturb sensitivity distribution patterns. Although for a given thoracic geometry the electrode configuration gives the overall sensitivity distribution features, sharp large local changes occur near the boundaries between different tissues in the heterogeneous model. The results of sensitivity distributions of the heterogeneous thoracic model demonstrate the feasibility of impedance source localization. Selectivity can be used to as a guide to finding favorable electrode configuration for regional impedance monitoring.